Historically, livestock waste, particularly in solid form, has been spread on the surface of the soil by a manure spreader using a flail to fling the material to the rear. A more modern side-discharge spreader also deposits the material on the surface of the soil.
The advent of confinement systems for animals which include pits below the confinement area, produces a large amount of animal waste in a slurry form which must be handled and disposed of. Typically, the slurry is pumped in a large tank carried by a wagon, but originally it was for the most part, spread or sprayed on the surface of the soil.
This procedure has, as a principle objection, a strong odor which remains after the waste is spread. Moreover, surface spreading of animal waste is not desirable with the potential runoff of nitrates and phosphorus into rivers and streams or seeping of the material into ground water sources. This is objectionable because livestock waste is high in nitrogen, and swine waste is also high in phosphorus, and with increasing concern with the quality of drinking water, this procedure is becoming less and less acceptable.
Various methods have been proposed for depositing the slurry underground. One method is to use a fertilizer knife, such as shown in U.S. Pat. No. 4,592,294, and to weld a large pipe to the rear of the knife to deliver the slurry behind the knife and into the slot cut in the soil by the knife. This leaves a very narrow band of fertilizer having a high concentration of nitrogen and other nutrients.
Another method of subsoil delivery of animal waste employs a standard chisel plow shank with an attached wide cultivator sweep, in an attempt to distribute the slurry further laterally and to avoid the concentration which occurs in the case of a simple fertilizer knife, described above.
This method, however, has not fully overcome the concentration problem, and it presents still another problem—namely, the cultivator sweep unnecessarily tills the soil and may result in burying surface residue. This may be a separate problem, particularly for farmers whose land may have been designated HEL, because there are federal requirements to maintain a certain percentage of crop residue on the surface of such soil. Both the chisel plow shank (which is a wide shank) and cultivator sweeps are designed to create a plowing action that mixes the soil with the residue, buries a large percentage of the residue, and leaves a furrow behind the shank.
A more recent improvement is disclosed in U.S. Pat. No. 5,865,131. This device uses a spring-cushioned colter running ahead of the applicator for cutting an initial slot in residue and providing a break line in the soil to be parted by a trailing shank. The shank spreads the initial slot and deepens it. The shank includes a shoe provided with a pair of wings extending laterally. The shoe is in the form of a tillage point which fractures and lifts the soil in front of the shank. The wings lift the soil laterally of the shank from the center toward the outward ends of the wings to provide slots for promoting lateral distribution of the slurry.
The applicator of the '131 patent is suitable for delivering higher application rates of slurry, in the range of 9,000 to 10,000 or more gallons per acre. However, the ground speed of the '131 patent is limited to a range of 3–5 miles per hour. At these slower speeds, the soil is lifted sufficient to form lateral fissures in the soil at a depth of approximately 3 to 4 inches which permits the slurry to flow laterally of the applicator shank. Any greater speed would cause too much soil disruption, lifting and redistribution (i.e. tillage) due to the use of a forward portion of the shoe which acts like a plow point, having a surface which is inclined upwardly and rearwardly for fracturing and lifting the soil in front of the shank.
Current regulations for the application of slurry fertilizer to agricultural land limit the rates of slurry in the range of 3,400 to 5,000 gallons per acre. This lower application rate enables operators to run at higher ground speeds, greater than 5.0 miles per hour, and up to 8.0 miles per hour. On the other hand, if the apparatus of the '131 patent were run at a substantially higher speed, due to its structure, and primarily due to a leading point or shoe which had an inclined nose extending upwardly and rearwardly from the leading edge, it would create a lifting of the soil after fracturing it. At higher speeds the '131 device acts like the shank of a chisel plow, not only creating substantial turbulence in the soil, but burying surface residue, which, in certain applications mentioned above is undesirable.